Controller for providing an efficient dormant mode for a group communication network

ABSTRACT

A method and apparatus for providing an efficient dormant mode for push-to-talk communication devices in a group communication network provides for determining whether the net has been inactive for a predetermined first time period and, if so, causing each member of the net to enter a control-hold mode, wherein each member of the net maintains its dedicated traffic channel. The method further includes the steps of determining whether each member of the net has been in the control-hold mode for a predetermined second time period and, if so, causing each member of the net to enter a dormant mode, wherein each member of the net releases its dedicated traffic channel. The method and apparatus further provides for causing each member of the net to cache its service configuration state before entering the dormant mode.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/291,454, filed May 15, 2001, which isincorporated herein by reference in its entirety.

FIELD

[0002] The present invention relates to point to multi-pointcommunications systems. More specifically, the present invention relatesto a method and apparatus for providing an efficient dormant mode forpush-to-talk communication devices in a group communication network.

BACKGROUND

[0003] A class of wireless service intended for quick, efficient,one-to-one or one-to-many (group) communication has existed in variousforms for many years. In general, these services have been half-duplex,where a user presses a “push-to-talk” (PTT) button on his phone/radio toinitiate speech. Pushing the button either keys his radio, in someimplementations, or in a moderated system, where communications occursvia a server of some type, indicates the user's request for the “floor.”If granted the floor, or talker permission, the user then generallyspeaks for a few seconds, after which he releases his PTT button, andother speakers can request the floor. Communication is generally fromone speaker to a group of listeners, but may be one-to-one. This servicehas traditionally been used in applications where one person, a“dispatcher,” needs to communicate to a group of people, such as fieldservice personnel or taxi drivers, which is where the “dispatch” namefor the service comes from.

[0004] Recently, similar services have been offered on the Internet andare generally known as “voice chat.” These services are usuallyimplemented as personal computer applications that send vocoder framesin Internet protocol (IP) packets, i.e., voice-over-IP (VoIP) service,to a central group chat server, or possibly from client to client in apeer-to-peer service.

[0005] A key feature of these services is that communication is quickand spontaneous, usually initiated by simply pressing a PTT button,without going through a typical dialing and ringing sequence.Communication in this type of service is generally very short, withindividual talk “spurts” being generally on the order of severalseconds, and “conversations” lasting possibly a minute or less.

[0006] The time delay between when the user requests the floor and whenhe receives a positive or negative confirmation from the server that hehas the floor and may begin speaking, which is known as the PTT latency,is a critical parameter for half-duplex group communications systems. Asmentioned previously, dispatch systems place a priority on short, quickconversations, which makes the service less effective if the PTT latencybecomes large.

[0007] Existing group communication infrastructures provide limitedopportunities for significantly reducing the PTT latency, i.e., actualPTT latency may not be possibly reduced below the time required tore-establish traffic channels within dormant packet-data sessions.Further, talker and listeners traffic channels are brought up in series,because the only mechanism available to begin waking up a dormant groupis to wait for the talker's traffic channel to be reestablished tosignal the server. Currently, no mechanism exists to sendmobile-originated user signaling data on anything other than a trafficchannel—a limitation that requires traffic channels to be re-establishedbefore any communication between clients and the server can take place.

[0008] There is a need, therefore, for mechanisms to reduce bothapparent PTT latency experienced by the talker and total time requiredto re-establish traffic channels for participating mobiles withoutnegatively impacting system capacity, client battery life, or otherresources.

SUMMARY OF THE INVENTION

[0009] The disclosed embodiments provide a novel and improved method andapparatus for providing an efficient dormant mode for push-to-talkcommunication devices in a group communication network. In one aspect ofthe invention, a method for providing an efficient dormant mode includesthe steps of determining whether the net has been inactive for apredetermined first time period and, if so, causing each member of thenet to enter a control-hold mode, wherein each member of the netmaintains its dedicated traffic channel. The method further includes thesteps of determining whether each member of the net has been in thecontrol-hold mode for a predetermined second time period and, if so,causing each member of the net to enter a dormant mode, wherein eachmember of the net releases its dedicated traffic channel.

[0010] In another aspect of the invention, a method for providing anefficient dormant mode for push-to-talk communication devices in a groupcommunication network includes the steps of determining whether the nethas been inactive for a predetermined time period, causing each memberof the net to enter the dormant mode if it is determined that eachmember of the net has been inactive for the predetermined time period,and causing each member of the net to cache a state of its serviceconfiguration before entering the dormant mode.

[0011] In another aspect of the invention, a controller for providing adormant mode for push-to-talk communication devices in a groupcommunication network includes a receiver, a memory unit, a transmitter,and a processor communicatively coupled with the receiver, the memoryunit, and the transmitter. The processor is capable of performing theabove steps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The features and advantages of the present invention will becomemore apparent from the detailed description set forth below when takenin conjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

[0013]FIG. 1 illustrates a group communications system;

[0014]FIG. 2 illustrates how several communication devices interact witha communications manager;

[0015]FIG. 3 illustrates call-signaling details for a floor-controlrequest process according to one embodiment;

[0016]FIG. 4 illustrates call-signaling details for a network-initiateddormancy-wakeup process according to one embodiment;

[0017]FIG. 5 illustrates buffering media at a communications managerside according to one embodiment;

[0018]FIG. 6 illustrates buffering media at a client side according toone embodiment; and

[0019]FIG. 7 illustrates exemplary radio-link modes according to oneembodiment.

DETAILED DESCRIPTION

[0020] Before one embodiment of the invention is explained in detail, itis to be understood that the invention is not limited in its applicationto the details of the construction and the arrangement of the componentsset forth in the following description or illustrated in the drawings.The invention is capable of being implemented in other embodiments andare carried out in various ways. Also, it is understood that thephraseology and terminology used herein is for purpose of descriptionand should not be regarded as limiting.

[0021]FIG. 1 illustrates an exemplary functional block diagram of agroup communication system 100. The group communication system 100 isalso known as a push-to-talk system, a net broadcast service (NBS), adispatch system, or a point-to-multi-point communication system. In theNBS 100, a group of communication device users, individually known asnet members, communicate with one another using a communication deviceassigned to each net member. The term “net” denotes a group ofcommunication device users authorized to communicate with each other.

[0022] In one embodiment, a central database may contain informationidentifying the members of each particular net. More than one net mayoperate in the same communication system. For instance, a first net maybe defined having ten members and a second net may be defined, havingtwenty members. The ten members of the first net may communicate witheach other, but may not communicate with members of the second net. Inanother embodiment, members of different nets are able to monitorcommunications between members of more than one net, but may be onlyable to transmit information to members within their own net.

[0023] A net may operate over an existing communications system, withoutrequiring substantial changes to the existing infrastructure. Thus, acontroller and users on a net may operate in any system capable oftransmitting and receiving packet information using Internet protocol(IP), such as a Code Division Multiple Access (CDMA) system, a TimeDivision Multiple Access (TDMA) system, a Global System for MobileCommunications (GSM) system, satellite communication systems such asGlobalstar™ or Iridium™, or a variety of other systems.

[0024] Net members may communicate with each other using an assignedcommunication device, shown as communication devices (CDs) 102, 104, 106and 108. CDs 102, 104, 106 and 108 may be wireline or wirelesscommunication devices such as terrestrial wireless telephones, wirelinetelephones having with push-to-talk capability, satellite telephonesequipped with push-to-talk functionality, wireless video cameras, stillcameras, audio devices such as music recorders or players, laptop ordesktop computers, paging devices, or any combination thereof. Forexample, the CD 102 may comprise a wireless terrestrial telephone havinga video camera and display. Furthermore, each CD may be able to send andreceive information in either a secure mode, or a non-secure (clear)mode. Throughout the following discussion, reference to an individual CDinfers a wireless push-to-talk phone. However, it should be understoodthat reference to a CD is not intended to be limited as such, and mayencompass other communication devices that have the capability totransmit and receive packet information in accordance with the InternetProtocol (IP).

[0025] In the NBS system 200 of FIG. 2, a transmission privilegegenerally allows a single user to transmit information to other netmembers at a given time. The transmission privilege is granted or deniedto a requesting net member, depending on whether or not the transmissionprivilege is currently assigned to another net member when the requestis received. The process of granting and denying transmission requestsis known as arbitration. Arbitration schemes may evaluate factors suchas priority levels assigned to each CD, the number of unsuccessfulattempts to gain transmission privilege, the length of time a net memberhas held transmission privilege, or other factors, in determiningwhether a requesting net member is granted the transmission privilege.

[0026] In order to participate in the NBS system 100, CDs 102, 104, 106,and 108 each may have the ability to request transmission privilege froma controller or a communications manager (CM) 110. CM 110 may manage thereal-time and administrative operation of nets. The CM is any type ofcomputer type device having at least one processor and memory. In oneembodiment, the CM is a Sun Workstation Netra T1™.

[0027] CM 110 may operate remotely through either a communication systemservice provider, net members, or both, assuming that authorization isprovided by the service provider. CM 110 may receive net definitionsthrough an external administration interface. Net members may requestadministrative actions through their service provider or administratenet functions through defined systems, such as a member-operatedsecurity manager (SM) 112 that conforms to a CM administrationinterface. CM 110 may authenticate the party who attempts to establishor modify a net.

[0028] SM 112 may perform key management, user authentication, andrelated tasks to support secure nets. A single group communicationsystem may interact with one or more SM 112. SM 112 may not be involvedin the real-time control of a net, including net activation or PTTarbitration. SM 112 may have administration capabilities compatible withCM 110 interface to automate administration functions. SM 112 may alsobe capable of acting as a data endpoint for the purpose of participatingin a net, broadcast net keys, or simply monitor net traffic.

[0029] In one embodiment, the means for requesting the transmissionprivilege from a CM comprises a push-to-talk (PTT) key or switch. When auser in the NBS 100 desires to transmit information to other netmembers, the user may depress the push-to-talk switch located on his orher CD, sending a floor-control request to obtain the transmissionprivilege from CM 110. If no other net member is currently assigned thetransmission privilege, the requesting user may be granted thetransmission privilege and the user may be notified by an audible,visual, or tactile alert through the CD. After the requesting user hasbeen granted the transmission privilege, information may then betransmitted from that user to the other net member.

[0030] In one embodiment of the present invention, each wireless netmember establishes a forward link and a reverse link with one or morebase stations 116 or a satellite gateway 118, as the case may be. Basestation 116 may be used to describe a communication channel from basestation 116 or satellite gateway 118 to a CD. Satellite gateway 118 maybe used to describe a communication channel from a CD to base station116 or satellite gateway 118. Voice and/or data may be converted intodata packets, using a CD, for example, which are suitable for aparticular distributed network 120 through which communications to otherusers may take place. In one embodiment, distributed network 120 is theInternet.

[0031] In one embodiment, a dedicated forward channel is established ineach communication system, i.e., a terrestrial communication system anda satellite communication system, for broadcasting information from eachnet member to the other net members. Each net member may receivecommunications from other net members over the dedicated channel. Inanother embodiment, a dedicated reverse link is established in eachcommunication system for transmitting information to CM 110. In oneembodiment, a combination of the above schemes may be used. For example,a scheme may involve establishing a dedicated forward broadcast channelbut requiring wireless CDs to transmit information to CM 110 over adedicated reverse link assigned to each CD.

[0032] When a first net member wishes to transmit information to othermembers of the net, the first net member may request the transmissionprivilege by pressing a push-to-talk key on his or her CD, whichgenerates a request formatted for transmission over the distributednetwork 120. In the case of CDs 102 and 104, the request may betransmitted over the air to one or more base stations 116. A mobileswitching center (MSC) 122, which may include a well-known interworkingfunction (IWF), packet data serving node (PDSN), or packet controlfunction (PCF), for processing data packets may exist between BS 116 andthe distributed network 120. For CD 106, the request is transmitted viasatellite gateway 118. For CD 108, the request may be transmittedthrough the public switched telephone network (PSTN) 124 to a modem bank126. Modem bank 126 receives the request and provides it to distributednetwork 120. An NBS terminal 128 monitors traffic of the NBS systemthrough its connection to distributed network 120. Since NBS terminal128 is connected to the distributed network 120, geographic proximity tonet participants is not necessary.

[0033] If no other member currently holds the transmission privilege,when the CM 110 receives a transmission privilege request, CM 110 maytransmit a message to the requesting net member, notifying it that thetransmission privilege has been granted. Audio, visual, or otherinformation from the first net member may then be transmitted to theother net members by sending the information to CM 110, using one of thejust-described transmission paths. In one embodiment, CM 110 thenprovides the information to the other net members by duplicating theinformation and sending each duplicate to the other net members. If asingle broadcast channel is used, the information need only beduplicated once for each broadcast channel in use.

[0034] In an alternative embodiment, CM 110 is incorporated into MSC 122so that data packets from supporting base stations are routed directlyto CM 110 without being routed onto distributed network 120. In thisembodiment, CM 110 is still connected to distributed network 120 so thatother communication systems and devices may participate in a groupcommunication. In yet another embodiment, the CM may be incorporatedinto the PDSN or the PCF modules of the MSC.

[0035] In one embodiment, CM 110 maintains one or more databases formanaging information pertaining to individual net members as well as toeach defined net. For example, for each net member, a database maycomprise information such as the user name, account number, a telephonenumber, or dial number, associated with the member's CD, a mobileidentification number assigned to the CD, the current member's status inthe net, such as whether the member is actively participating in thenet, a priority code for determining how the transmission privilege isassigned, a data telephone number associated with the CD, an IP addressassociated with the CD, and an indication of which nets the member isauthorized to communicate with. Other related types of information mayalso be stored by the database with respect to each net member.

[0036] In one embodiment, the CD may form connections of individualcommunication terminals to form one talk group, or net. The CM maycomprise a variety of functional capabilities in hardware and softwarethat are configurable in different ways to accommodate differentapplications. The CM may provide capability to manage real-time,administrative, and authenticity operations of (NBS) nets, push-to-talk(PTT) request arbitration, maintenance and distribution of netmembership and registration lists, call set-up and tear-down ofnecessary communication, e.g., CDMA, systems and network resources, aswell as overall control of net status.

[0037] The NBS net may be within a stand-alone deployable cellularsystem, or a large multiple site configuration. In the case of a largeconfiguration, multiple CMs may be deployed geographically to form asingle, integrated system, each operating as a plug-in module intoexisting cellular infrastructure. As such, new features introduced byNBS nets are available to cellular users without requiring modificationto existing cellular infrastructure.

[0038] The CM may maintain a list of defined NBS nets. In oneembodiment, each net definition includes a net identifier, a list ofmembers, including phone numbers or other identifying information, userpriority information, and other generic administration information. Netsmay be statically defined as either clear or secure, and transitionsbetween clear and secure may not be permitted. A secure NBS nettypically uses media encryption to provide authentication and guardagainst eavesdropping. Media encryption for secure nets is implementedon an end-to-end basis, meaning encryption and decryption may take placewithin the communication device. The CM may operate without knowledge ofsecurity algorithms, keys, or policies.

[0039]FIG. 2 illustrates an exemplary NBS net 200 for showing how acommunication device 202 interacts with a CM 204. Multiple CMs may bedeployed as desired for large-scale NBS nets. In FIG. 2, CD 202 haspermission to transmit media to other members of the net. In this case,CD 202 is known as the talker and transmits media over a channel. WhenCD 202 is designated as the talker, the remaining net participants, CD206 and CD 208, may not have permission to transmit media to the net.Accordingly, CD 206 and CD 208 are designated as listeners.

[0040] As described above, CD 202, 206, and 208 are connected to CM 204,using at least one channel. In one embodiment, the channel is dividedinto separate channels comprising a session initiation protocol (SIP)channel 210, a NBS media signaling channel 212, and a media trafficchannel 214. SIP channel 210 and NBS media signaling channel 212 may beused at any time as bandwidth allows by any of the CDs 202, 206, and208, regardless of being designated a talker or a listener. The SIP isan Internet engineering task force (IETF) defined application-layerprotocol that describes control mechanisms to establish, modify, andterminate multimedia sessions operating over Internet protocol (IP). SIPprovides a general solution to call-signaling problems for Internettelephony applications by supporting mechanisms to register and locateusers, mechanism which define user capabilities and describe mediaparameters, and mechanisms to determine user availability, call setup,and call-handling.

[0041] In one embodiment, SIP channel 210 is used to start and endparticipation of a CD within the NBS net 100. A session descriptionprotocol (SDP) signal may also be used within SIP channel 210. When theCD's participation within the NBS net is setup, e.g., by using SIPchannel 210, real-time call control and signaling between the CD and theCM takes place, e.g., by using NBS media signaling channel 212. In oneembodiment, NBS media signaling channel 212 is used to handlepush-to-talk requests and releases, arbitrate between conflictingrequests, or floor control, announce the beginning and end ofinformation transmission, manage net dormancy, track endpointconnectivity, request and exchange net status, and notify any errormessages. The protocol of NBS media signaling channel 212 minimizes thelength of most common messages, and simplifies the task of interpretingreplies and responding to requests while retaining flexibility forfuture enhancements. The protocol of NBS media signaling channel 212also allows requests to be resent without adversely affecting protocolstate.

[0042] In one embodiment, signaling traffic on NBS media channel 212includes call setup and control signaling, which may consist of sessioninvitation requests and acknowledgements, and media signaling, which maycomprise of real-time floor control requests and related asynchronousmessages. Media traffic on the media traffic channel 214 may comprise ofreal-time point-to-multi-point voice and/or data broadcasts. Bothmessaging categories have unique functional attributes. In addition,each CD may issue domain name service (DNS) client requests tofacilitate mapping fully qualified DNS hostnames to Internet networkaddresses.

[0043] In one embodiment, the NBS call-setup and call-control signalingis performed according to SIP semantics. Although SIP may be transportedusing either the well-known user datagram protocol (UDP) or transmissioncontrol protocol (TCP), in one embodiment, each CD performs SIP basedsignaling functions using UDP. Also, each CM may expect to receive SIPsignaling requests via UDP. Real-time signaling may occur via dynamicUDP/IP interface on the CM and each CD. Other signaling may take placevia a fixed TCP/IP interface between the CM and the CD using the SIP,for example.

[0044] PTT Latency

[0045] In one embodiment, when the packet data service is active,resources in the infrastructure, e.g., base station transceiversubsystem (BTS), base station controller (BSC), interworking (IWF), andthe radio link are actively assigned to the mobile station (MS). In anIP-based VoIP dispatch service, while there is an active conversationgoing on between group participants, the packet data connection for eachuser remains active. However, after a period of inactivity, i.e., “hangtime,” in the group communications the user traffic channels maytransition to the dormant state.

[0046] The transition to the dormant state conserves system capacity,reduces serverice cost and battery drain, and makes the user availableto receive incoming conventional voice calls. For example, when the useris in an active packet data call, he will generally be considered to be“busy” to incoming voice calls. If the user's packet data call is in thedormant state, the user may be able to receive incoming voice calls. Forthese reasons, it is desirable to transition the packet data call to thedormant state after periods of packet data inactivity.

[0047] While packet data calls are active, even if no data packets arebeing exchanged, radio frequency (RF) energy may still be transmitted bythe mobile phones, albeit at a low level, to maintain synchronizationand power control with the base station. These transmissions may cause asignificant power drain on the phone. In the dormant state, however, thephone may not perform any RF transmission. To conserve phone power andextend battery life, the hang time may be set to transition the phone todormant mode after extended periods of no data transmission.

[0048] While the packet data service is active for all users, PTTrequests, which may be IP datagrams sent between the MS and the dispatchserver, have very low latency. However, if the user channels havepreviously transitioned to the dormant state, the PTT latency may bemuch longer. During packet data dormancy, state information associatedwith the packet data session, including the mobile IP address, may bemaintained. However, state information associated with layers below PPP,such as the physical traffic layers, may be released and/orde-allocated.

[0049] In some infrastructures, to wake up a dormant data connection,the traffic channel must be reallocated, the resources must bereassigned, and the radio link protocol (RLP) layer must bereinitialized. The effect of this is that after a talk group has nottalked for a while, when a user presses his PTT button to request thefloor, the PTT latency for the first talk spurt is generally much longerthan for subsequent talk spurts. While this is relatively infrequent, itcan affect the utility of the service, and should be minimized.

[0050] In one embodiment, when the group communication devices are inthe dormant state, PTT latency may be caused by the following:

[0051] 1. Talker Channel Assignment Delay—Delay in assigning andinitializing a traffic channel for the talker's phone in response to auser pushing a push-to-talk button and the dispatch applicationinitiating an IP-based floor-request message.

[0052] 2. Floor Request Propagation Delay—Time for a floor-requestmessage to propagate to the dispatch server.

[0053] 3. Arbitration Delay—Time for the dispatch server to processpotentially multiple floor requests.

[0054] 4. Wakeup Message Delay—Time for the IP messages from thedispatch server to propagate to the cellular infrastructure, e.g., PDSN,serving the listener.

[0055] 5. Listener Paging Delay—Time delay due to the requirement towait for the listener's phone to wake up and recieve a page in theappropriate paging channel slot.

[0056] 6. Listener Channel Assignment Delay—Delay in assigning andinitializing the traffic channels of the listeners' phones.

[0057] Some of these delays are more significant than others in theircontribution to the overall PTT latency. For instance, the talker andlistener channel assignment latencies, and the listener paging latencyare often an order of magnitude greater than the other components, andtogether drive the ultimate PTT latency performance.

[0058] To reduce the PTT latency, in one embodiment, the group callsignaling, such as the floor-control requests, floor-control responses,and dormancy wakeup messages, may be transmitted on some availablecommon channels, without waiting for dedicated traffic channels to bere-established. Such common channels may be always available, regardlessof the state of the mobiles, and may not require being requested andreassigned each time a user wishes to initiate a group call. Therefore,the group call signaling may be exchanged even when mobiles are dormant,which may provide a means to re-establish dedicated traffic channels forthe talker and listener mobiles in parallel.

[0059] In one embodiment, the calling mobile may send a floor-controlrequest to the wireless infrastructure over some available reversecommon channels, such as reverse access channel and reverse enhancedaccess channel. The calling mobile may also receive a response to thefloor-control request on some available forward common channels, such asforward paging channel and forward common control channel. In oneembodiment, the dormant listener mobiles may receive dormancy wakeupmessages on some available forward common channels, such as forwardpaging channel and forward common control channel.

[0060] Short Data Burst Call-Signaling Messages

[0061] In one embodiment, a significant reduction in the actual totaldormancy wakeup time and the PTT latency perceived by the talker, may beachieved through the use of the short data burst (SDB) messages, asprovided in “TIA/EIA/IS-2000 Standards for cdma2000 Spread SpectrumSystems,” hereinafter referred to as “the cdma2000 standard,” forexample. In one embodiment, SDB messages may be sent over both dedicatedphysical channels, such as the forward fundamental channel (FCH) orforward dedicated common control channel (F-DCCH), or common physicalchannels, such as the reverse access channel (R-ACH), reverse enhancedaccess channel (R-EACH), forward common control channel (F-CCCH), orpaging channel (PCH). SDB messages may be transported by radio burstprotocol (RBP), which maps the messages onto an appropriate andavailable physical layer channel. Because SDB messages may carryarbitrary IP traffic and may be sent over common physical channels, SDBmessages provide a mechanism to exchange group call signaling when acalling client's mobile has no dedicated traffic channels.

[0062] Mobile-Originated Call-Signaling Messages

[0063] In one embodiment, media-signaling messages may carry IPdatagrams over the reverse link or mobile-originated link. A clientmobile station may signal the CM quickly whenever the user requests thefloor and a dedicated reverse traffic channel is not immediatelyavailable.

[0064] Assuming the client mobile station has released all dedicatedtraffic channels, the client mobile station may immediately forward thefloor-control request over a reverse common channel of a wirelessinfrastructure, which may relay the request to the CM. For example,either the reverse access channel or the reverse enhanced access channelmay be used to send such messages when a dedicated reverse channel isnot available. In one embodiment, the client mobile station may transmita floor-request message to the CM as an SDB Message.

[0065]FIG. 3 shows an exemplary call-signaling for a floor-controlrequest process. The client mobile station (MS) may receive a requestfrom a user who wishes to initiate a group call. In one embodiment, theclient MS may be a PTT device. In one embodiment, the client MS may sendthe PTT floor request 302 over a reverse common channel, such as theaccess channel or enhanced access channel, before attempting tore-establish its dedicated traffic channel. In one embodiment, theclient MS may send the PTT floor request 302 in a SDB message regardlessof what channel is used.

[0066] The client MS may then start re-establishing its dedicatedtraffic channel 304, e.g., by performing the “service option 33re-origination,” for example. The client MS may also start radio linkprotocol (RLP) synchronization 306. In one embodiment, the client MS mayreestablish its dedicated traffic channel and synchronize RLPadvantageously in parallel with sending the PTT floor request 302.

[0067] Therefore, use of the available reverse common channels and/orSDB feature to signal floor-control requests to the CM, when a mobilestation does not have active dedicated traffic channels, reduces thetotal time required to wake up the participating mobiles. Although thetalker client may not receive confirmation that its floor-request hasbeen granted until the talker's forward traffic channel isre-established, the ability to quickly signal the CM to begin waking upparticipating listeners reduces the overall latency.

[0068] Referring to FIG. 3, the wireless infrastructure may send the PTTfloor-control request 308 to packet data service node (PDSN) and then tothe CM. In one embodiment, after receiving the floor-control request310, the CM may arbitrate the request, burst media signaling wakeupmessages (triggers) to a group of target participants (listeners),and/or trigger the reestablishment of participants' (listeners') trafficchannels. If the CM grants the PTT floor request, the CM may send PTTfloor grant 312 to the infrastructure, which may send PTT floor grant314 to the client MS. In one embodiment, the infrastructure may send PTTfloor grant 314 to the client MS on an available forward common channel,such as forward paging channel and forward common control channel, ifthe client's dedicated traffic channel is not re-established yet. In oneembodiment, the infrastructure may send PTT floor grant 314 to theclient MS in SDB form regardless of what channel is used.

[0069] In one embodiment, the CM may wait for dormancy response timer toexpire before responding to the PTT floor-control request. If thegroup's dormancy response timer is set to zero, the CM may respond tothe floor-control request immediately. In one embodiment, if the clientMS has completed re-establishing its traffic channel and RLPsynchronization, the client MS may stream media 316, which may have beenbuffered in the client MS, to the CM.

[0070] Network-Originated Call-Signaling Messages

[0071] In one embodiment, after receiving the floor-control request, theCM may burst media signaling wakeup messages to a group of targetparticipants (listeners) and trigger the reestablishment ofparticipants' (listeners') traffic channels. If the group's dormancyresponse timer is set to zero, the CM may respond to the floor controlrequest immediately. In one embodiment, if the talker has beganre-establishing its traffic channel immediately upon sending the PTTrequest, the caller's and listeners' traffic channels may beadvantageously re-established in parallel.

[0072]FIG. 4 shows an exemplary call signaling for a network-initiateddormancy wakeup process. After the CM receives PTT floor-control request310 (FIG. 3), the CM may send wakeup triggers 402 directed to targetlisteners. The PSDN may determine whether a packet-data session existsfor the target mobile, and forwards the trigger packet to theappropriate infrastructure element, e.g., a base station. Theinfrastructure may page 406 each individual target MS to startre-establishing its dedicated traffic channel. The target MS may thenstart re-establishing its dedicated traffic channel 408, e.g., byperforming the “service option 33 re-origination,” for example. Thetarget MS may also start radio link protocol (RLP) synchronization 410.In one embodiment, the target MSs may re-establish their dedicatedtraffic channels and synchronize their RLPs advantageously in parallelwith same functions being performed by the client MS.

[0073] In one embodiment, after a target MS has completedre-establishing its dedicated traffic channel and synchronizing its RLP,the CM may resend the wakeup trigger 412 to the target MS. The target MSmay send the wakeup reply 414 to the CM, indicating that the target MSis ready to receive media. The CM may send talker announcement 416 tothe client MS before streaming media 418, which may have been bufferedin the CM, to the target MS.

[0074] In one embodiment, the infrastructure may send the wakeup trigger412 to a target listener over some available common forward channels,such as forward paging channel and forward common control channel, whilethe target listeners' traffic channels are not re-established yet. Inone embodiment, the infrastructure may send the wakeup trigger 412 tothe target listener in SDB form, regardless of what channel is used. Ifthe PTT floor-control request is sent on the talker's reverse commonchannel as a SDB message and the target group's dormancy response timeris set to zero at the CM, actual PTT latency at the talker client may bereduced to the time required to send an SDB request message on thereverse link followed by a SDB response message on the forward link.

[0075] Network Interfaces for Call-Signaling Messages

[0076] To determine what network-originated specific traffic, e.g., SDBpayload, is sent for an idle mobile station with no dedicated trafficchannels, some infrastructure policy or interface for distinguishingsuch specific traffic from other traffic may be implemented.

[0077] In a first embodiment, IP datagrams may be filtered based ontheir sizes, as the SDB messages may carry a limited user payload. IPdatagrams smaller than a predetermined size limit may be sent as SDBmessage, if destined for a mobile with no dedicated traffic channels.The group communication system may use such filters, as the applicationfloor-request response message is quite small, e.g., 34 bytes includingthe IP headers.

[0078] In a second embodiment, an infrastructure vendor may define anIP-based service for encapsulating IP traffic destined for delivery to amobile station. An IP server with knowledge of this service may transmitsmall IP, e.g., UDP, datagrams, appropriately encapsulated with IPheaders, to this service for delivery to a mobile suspected of nothaving a dedicated traffic channel. The group communication systems mayuse this service to indicate to the infrastructure that thefloor-request response message be delivered to the requesting client MSin SDB form, for example. Coordination of SDB traffic with pending pagesor service origination requests is also important to insure quick andreliable delivery of user traffic.

[0079] In a third embodiment, an IP server may transmit special IP,e.g., UDP, datagrams with IP headers for delivery to a mobile suspectedof not having a dedicated traffic channel. The IP server may tag the IPdatagrams, e.g., by designating a special value in the IP header, forinstructing the infrastructure to deliver the IP datagrams to the clientMS. The group communication systems may use this service to indicate tothe infrastructure that the floor-request response message be deliveredto the requesting client MS in SDB form, for example. In a thirdembodiment, a UDP or TCP port range may be reserved for deliveringspecific IP datagrams, e.g., SDB messages.

[0080] Mobile-Initiated Service Origination and Paging

[0081] In one embodiment, as discussed above in connection with FIG. 3,a talker mobile station (MS) may send a floor-control request 302 to theCM, which may be in SDB form, followed immediately with a serviceorigination request 304 to the wireless, e.g., CDMA, infrastructure forquickly re-establishing its traffic channels. However, if the dormancyresponse timer is set to a small value, the CM may respond to thefloor-control request 310 quickly and transmit a response 312 back tothe talker MS. If this response arrives at the infrastructure during theearly phases of the service origination transaction 304, theinfrastructure notes that the talker MS does not have any active trafficchannel and attempts to page the response to the talker MS. However,this paging action may abort the service origination transaction alreadyin progress. In one embodiment, the talker MS may respond to the page,insuring that the floor-control response message is delivered to thetalker, and request service origination again, but an unnecessary delayis experienced in re-establishing the talker's traffic channel as aresult of the aborted original service origination attempt.

[0082] In a first embodiment, to avoid the race condition between theservice origination process and paging, the CM may be configured to notrespond immediately to the floor-control request 310. Accordingly, thedormancy response timer, e.g., in the CM, may be adjusted so that the CMtransmits the response 312 to the talker MS after the serviceorigination process 304 is complete.

[0083] In a second embodiment, the PDSN, which receives the CM-initiatedresponse 312, and the mobile switching center (MSC), which responds tothe talker's service origination request, are coordinated. That is, ifthe PDSN determines that a packet-data service origination process forthe talker MS is already in progress when the CM-initiated response 312arrives at the infrastructure, the MSC may defer paging the talker MS.The PDSN may cache the response and send it over the talker mobile'sforward traffic channel once the service origination process iscomplete. Alternatively, the MSC may send the response to the talker MSas an SDB message if the service origination process is still inprogress.

[0084] In a third embodiment, the talker MS may avoid the race conditionby not issuing a service origination request 304 until after the talkerMS has received a response to the floor-control request 302. In oneembodiment, since the talker MS has no active dedicated traffic channel,the CM may send the response to the talker MS on some available forwardcommon channels, such as forward paging channel and forward commoncontrol channel. In one embodiment, the CM may send the response to thetalker MS in SDB form. The talker MS may rely on the CM-generatedfloor-control response 312 to trigger its traffic channel re-activation,in the same fashion that the wakeup requests sent by the CM triggertraffic channel re-activation for the listener mobiles. The racecondition is avoided as the potential for simultaneous mobile-initiatedservice origination and network-initiated paging of the mobile isavoided.

[0085] Caching Network-Initiated Packet Data Triggers

[0086] The IP datagram, including the wakeup trigger 402, that arrivesat the wireless, e.g., CDMA, infrastructure and is destined for alistener mobile that has no dedicated traffic channels may be lost,either by the network in general or by the wireless infrastructurespecifically. In one embodiment, the wakeup trigger 402 sent to thelistener mobile is retransmitted aggressively according to a definedschedule until the listeners respond or the group's wakeup timerexpires. For example, the wakeup trigger 402 may be resent every 500 ms.However, retransmitting the wakeup triggers 402 at this rate may cause amaximum delay of up to 500 ms, or an average delay of 250 ms, from thetime a listener's traffic channel is re-established to the time nextwakeup trigger destined for that listener arrives at the infrastructure.

[0087] In one embodiment, the infrastructure or another entity in thenetwork may cache the wakeup trigger 402 sent by the CM, and deliver itto a target MS as soon as the target MS has reestablished its trafficchannel. This eliminates the need for retransmission of wakeup request412 by the CM, and reduces total dormancy wakeup time. Cashing thewakeup trigger 402, as opposed to retransmitting it at the rate of 500ms, for example, may eliminate a delay of up to 500 ms from the totaldormancy wakeup time.

[0088] Media Buffering

[0089] In one embodiment, the user may be allowed to start talking afterthe user has requested floor control, by buffering the media beforededicated channels are re-established between the client and thelisteners. By buffering the talker's speech, the system allows thetalker to start talking before the listeners' traffic channels have beenfully re-established. This allows the talker to start talking earlier,reducing his apparent PTT latency. Since listeners don't experience PTTlatency, their experience is unaffected, i.e., the PTT latency isshifted from the talker to other parts of the system. The talker maywait just as long to receive a response from a listener to his firsttalk spurt, but as mentioned previously, he already expects the responseto his first talk spurt to take longer than the response to subsequenttalk spurts that occur while he is engaged in an active conversation.Buffering of the talker's first talk spurt can be done on the CM side oron the client MS side.

[0090] CM Buffering

[0091] In one embodiment, the CM may buffer the talker's first talkspurt. After a user has pressed his PTT button and the user's trafficchannels are re-established, he may be allowed to communicate with theCM. At this time, since the listener traffic channels are not yet up,the CM buffers the talker's speech for future transmission to the targetlisteners. CM buffering may reduce the apparent PTT latency that thetalker sees to the approximate time it takes to bring up the talker'straffic channel. FIG. 5 shows CM buffering according to one embodiment.

[0092] Client Side Buffering

[0093] In one embodiment, where a shorter apparent latency is desired,the talker may be allowed to begin speaking before even his trafficchannel is re-established. Because the client MS is not yet incommunication with the CM, the signal to the talker to begin talking ismade by the client MS. If the talker is allowed to speak before thetalker's traffic channel is reestablished, the client MS may buffer thespeech. Because communication with the CM has not yet been established,permission to talk is being given “optimistically.” FIG. 6 showsclient-side buffering according to one embodiment. In one embodiment,both CM buffering and client-side buffering may operate concurrently.Client-side buffering may allow the apparent PTT latency to be small.

[0094] As with CM buffering, the total delay may not alter. The user maystill experience the same delay in receiving a response back from thelistener, but the talker's apparent PTT latency may be made small.

[0095] In one embodiment, the client MS may buffer media to control theapparent PTT latency experienced by the user. The combination ofmobile-originated SDB and client-side media buffering may reduce thedelays associated with re-establishing active traffic channels.

[0096] Quick Paging Channel

[0097] In one embodiment, the CM may delay responding to the talker'sPTT request until the group's wakeup timer expires or all listenerclients have responded to a network-initiated trigger to bring up theirrespective traffic channels. The CM may wait until all listeners arepaged before allowing the talker to stream media at the group. Thelonger the group's listeners take to respond to the page, the longer thetalker's perceived PTT latency.

[0098] In one embodiment, during dormancy wakeup, each listener clientis individually sent a series of wakeup triggers by the CM, which uponarrival at the, e.g., CDMA, infrastructure, trigger one or more pages toeach mobile. After receiving the page, each mobile may re-establish atraffic channel, receive the next wake up request transmitted to it, andrespond to the CM with a wake up request reply. A major component of thetime required by listener handsets to respond to this application level“ping” is spent at the infrastructure waiting for an appropriate time topage the mobile.

[0099] To conserve battery life, mobiles may not need to constantlymonitor each of the, e.g., 2048, slots defined within the paging channelwhen the mobiles are in the idle state. Rather, mobiles may monitoreither the forward common control channel (F-CCCH) or the forward pagingchannel (F-PCH), depending on the mobile's capabilities. Furthermore,mobiles may monitor the paging slot according to their slot cycle index.

[0100] In one embodiment, to conserve battery life, the mobiles mayoperate in “slotted paging” mode. In this mode, the mobiles wake upperiodically for a short time to listen to pages sent by the basestation (BS). The BS, which may know when mobiles will be listening, maysend pages to a particular mobile during the particular paging slots.

[0101] In one embodiment, the period that the mobile wakes up to listento the paging channel is controlled by a parameter called the slot cycleindex (SCI). The larger the SCI, the longer the time between the slotsthat the mobile wakes up to listen to the paging channel. A large slotcycle value increases phone standby time, since the phone spends alarger percentage of its time sleeping, but increases the time the BSmight need to wait before it can page the phone.

[0102] The amount of time the BS may need to delay its page to the phonevaries between zero, if the phone's slot is just starting when the BSneeds to page it, to the full slot cycle, if the phone's slot has justended when to the BS needs to page the phone. On average, the delay dueto waiting for the phone's slot to come around is half the slot cycleperiod. The shorter the slot cycle used by a mobile, the faster alistener may be paged by the infrastructure. However, a shorter slotcycle may imply a higher rate of battery drain.

[0103] In one embodiment, the forward quick paging channel (F-QPCH) maybe used to allow the mobile to determine, in a power-efficient manner,when a pending page is present without requiring that the mobile monitorthe paging channel itself. A mobile that is capable of monitoring theF-QPCH may wake up every predetermined number of slots to extract thevalue of a one-bit indicator within a, e.g., 80 ms, slot on the pagingchannel. If the extracted bit is not set, no page is pending on thepaging channel and the mobile sleeps for another slot cycles. If theextracted bit is set, a page for that mobile may be pending and themobile may schedule itself to wake up and monitor the paging channel atthe next appropriate paging channel slot.

[0104] The modulation employed by F-QPCH allows the mobile to monitorthe F-QPCH much more efficiently than it can monitor the paging channel.This allows the mobile to effectively operate at a very short slot cyclein a power-efficient manner. One advantage of using the F-QPCH is toprovide the mobile with the means to detect and respond to general pagemessages from the infrastructure, and hence wakeup request messages fromthe CM, at a faster slot cycle than would otherwise be allowed at thesame battery drain rate. This in turn translates to the ability tominimize one component of the delay that contributes directly to PTTlatency and the total dormancy wakeup time—the time required tore-establish listener traffic channels.

[0105] Slotted Timer

[0106] In one embodiment, the mobiles may operate in a non-slottedpaging mode in conjunction with a “slotted timer.” When activated, theslotted timer requires the mobile to monitor the paging channel in anon-slotted mode upon releasing its dedicated traffic channels andentering the idle mode for a period of time defined by the slottedtimer. The value of this timer is configurable at the base station. Thisfeature allows the infrastructure to instruct the mobile to monitorevery, e.g., 80 ms, slot on the paging channel when in the idle mode andprovides a means for the infrastructure to page the mobile in any slot.As in the case of using the quick paging channel feature alone, oneadvantage of using the non-slotted mode is to provide a means for themobile to detect and respond to pages more quickly than would otherwisebe allowed at the same battery drain rate, and hence to reduce the timerequired to re-establish listeners' traffic channels during dormancywakeup.

[0107] Without the quick paging channel feature, extended use ofnon-slotted monitoring may be expensive on battery life. However, usingthe quick paging channel and non-slotted mode together provides a meansto page a mobile almost immediately-within one or two slot periods,e.g., 80 to 160 ms.

[0108] Non-slotted mode can be viewed as one of two intermediate stagesof dormancy available to a mobile station. When operating in non-slottedmode, a mobile may be considered technically dormant because it has nodedicated physical channels. However, in this mode the mobile may bepaged essentially immediately in any slot, and thus the paging delayassociated with network-initiated reactivation is avoided.

[0109] Control-Hold Mode

[0110] In one embodiment, the mobiles may operate under a packet datastandard that provides an additional dormant/idle state in which themobile and infrastructure maintain the PPP layer state associated withthe mobile while allowing either endpoint to release the dedicatedtraffic channels and other resources associated with the mobile'spacket-data service option call. Either the mobile or the infrastructuremay transition the state of the packet data call from dormant/idle stateto active state by re-establishing a traffic channel and renegotiatingRLP. The time required to re-establish the traffic channel may bedependent on whether the mobile or the infrastructure initiates there-establishment. However, in both cases the delay is comparable to thatrequired to originate a new call on the system, as essentially allsystem resources may need to be requested and allocated to the mobile.

[0111] In one embodiment, the mobiles may operate in a “control-hold”mode that operates as an interim position between the active and idlemodes. In control-hold mode, the dedicated traffic channels associatedwith the mobile may be released and the mobile's reverse pilot mayoperate in “gated” mode. In one embodiment, the dedicated common controlchannel and/or the RLP state may also maintained. In essence, thecontrol-hold mode offers a semi-dormant state in which most systemresources may remain allocated, but the average reverse-linktransmission power is reduced to a gated pilot in order to reduce theimpact to system capacity. FIG. 7 shows an exemplary arrangement forradio modes.

[0112] In one embodiment, mobiles may transition from active mode tocontrol-hold mode by sending either a resource release request messageor a resource release request mini message. Mobiles may transition fromcontrol-hold mode to active mode by sending either a resource requestmessage or a resource request mini message. These messages may betransported via the dedicated control channel, and the mini-messages maybe sent using shorter, e.g., 5 ms, frames, allowing fast transitionsinto and out of control-hold mode. On advantage of the control-holdmode, compared to the traditional idle mode or the dormant/idle mode, asdescribed above, is the relatively fast transition possible fromcontrol-hold mode to active mode.

[0113] In one embodiment, upon receiving an indication from the CM thata subscribed group has transitioned to the group-dormant state, a clientmobile may initially transition itself to the control-hold mode and,after an additional sustained period of inactivity, make a furthertransition to the idle mode. Therefore, control-hold mode offers amechanism to significantly reduce the time required to re-establishdedicated traffic channels once a user presses PTT or a wakeup requesttrigger is received at the infrastructure.

[0114] Stored Service Configuration

[0115] In one embodiment, the infrastructure may provide the ability tocache or store service configuration state at the mobile andinfrastructure when transitioning to idle mode. When returning back tothe active mode and re-establishing traffic channels, the mobile mayindicate, in either the origination message or page response message,that it has cached or stored a service configuration for the call. Themobile may also include in the origination or page response message acyclic redundancy check (CRC) that may be calculated over the entirelength of the service configuration. If the base station has also cachedthe service configuration, the base station may use the received CRC toconfirm that its service configuration matches the mobile's storedservice configuration and, if so, the BS may indicate in its “serviceconnect message” that the mobile may use the previously stored serviceconfiguration.

[0116] In one embodiment, the use of the packet-data service option maynot require service configuration changes when transitioning out of theidle mode, and hence use of the stored service configuration may resultin a significant reduction in the time-required to re-establishdedicated traffic channel resources. Therefore, the stored serviceconfiguration feature implements an important enhancement to the idlemode by providing a mechanism to significantly reduce PTT latency byreducing the time required to re-establish traffic channels which maycarry both PTT signaling and related media.

[0117] In one embodiment, the transition to the idle mode from theactive mode for a client MS may be implemented as follows:

[0118] 1. The group is active and the mobile has dedicated trafficchannels.

[0119] 2. After a period of inactivity exceeding the group's hang timetimer, an application layer group-dormant announcement is received overthe mobile's forward traffic channel.

[0120] 3. The mobile transitions to the control-hold mode, caching thestate of its service configuration. Likewise, the client's base stationalso caches the state of the service configuration.

[0121] 4. After a period of inactivity, the mobile releases itsdedicated channel and transitions to the idle mode. The mobile beginsmonitoring the quick paging channel and may enter non-slotted mode ifinstructed by the infrastructure. If the period of inactivity isrelatively short - either due to the local user pressing PTT ornetwork-originated packet data traffic from another groupparticipant—the mobile may not reach the idle mode before transitioningback to the active mode. In this case, the transition back to the activemode occurs quickly, as the mobile has retained its dedicated channel.

[0122] In one embodiment, the dormancy wakeup event may be implementedas follows:

[0123] 1. The group is dormant and all the mobiles are idle with nodedicated physical channels. The mobiles are monitoring the quick pagingchannel.

[0124] 2. In response to a user pressing push-to-talk, the talker'smobile signals the CM with an application layer floor-request messageover some available reverse common channel, which may be in short databurst form. The talker's mobile may begin buffering user media from thispoint forward.

[0125] 3. The talker's mobile sends an “origination message” to theinfrastructure to reestablish its traffic channel. It may indicate inits request that it has cached the service configuration and may includea CRC over the configuration data. This begins the process ofre-establishing the talker's mobile traffic channel.

[0126] 4. The CM receives the floor-request and decides whether to grantthe request or not, through an arbitration process and sendsfloor-request response messages to the talker. The CM also beginsbursting a series of wakeup requests to all participants.

[0127] 5. Upon receipt of each wakeup request, the infrastructure pageseach listener's mobile by first determining the next appropriate slot inwhich to page the listener's mobile and then signaling via the F-QPCHprior to that slot that a page will be pending on the paging channel forthat listener's mobile.

[0128] 6. Upon receipt of an indication on the F-QPCH that a page ispending, each listener mobile monitors the paging channel for a page.

[0129] 7. Upon receipt of a page on the paging channel, each listenermobile responds to the page, indicating in its page response that it hascached the service configuration and may include a CRC over theconfiguration data. This begins the process of re-establishing eachlistener's traffic channel.

[0130] 8. After establishment of the talker's traffic channel, the nextfloor-request response from the CM is received at the talker. The talkerbegins streaming media to the CM.

[0131] 9. After establishment of each listener's traffic channel, thenext wakeup request sent by the CM is received at the listener. Thelistener replies with a wakeup response message.

[0132] 10. Once all listeners have responded or the group's wakeup timerexpires, the CM begins streaming media to the group.

[0133] Therefore, the herein disclosed embodiments for a method andapparatus for reducing latency in a group communication network providesfor a significant reduction in the actual total dormancy wakeup time andthe PTT latency by exchanging group call signaling even when mobiles aredormant and no traffic channel is active. The method and apparatusprovides for exchanging the group call signaling through the use of theshort data burst (SDB) message signaling. The method and apparatusprovides for re-establishing dedicated traffic channels for the talkermobile and the dormant listener mobiles advantageously in parallel.

[0134] In another embodiment, the dormant-wakeup latency in a groupcommunication network may be reduced through caching thenetwork-initiated wakeup triggers destined for target listeners, anddelivering a wakeup trigger to a target mobile station as soon as thetarget mobile station has re-established its traffic channel.

[0135] In another embodiment, simultaneous service origination andpaging in a mobile operating in a group communication network is avoidedby transmitting a response to a floor-control request after the serviceorigination process is complete. In one embodiment, the response to thefloor-control request may be in SDB form if the service originationprocess is not complete. In another embodiment, the service originationprocess for the source communication device is initiated aftertransmitting the response to the source communication device.

1. In a controller operating in a group communication network, a methodfor putting a net into a dormant mode, the method comprising:determining whether the net has been inactive for a predetermined firsttime period; if it is determined that the net has been inactive for thepredetermined first time period, causing each member of the net to entera control-hold mode, wherein said each member of the net maintains itsdedicated traffic channel; determining whether said each member of thenet has been in the control-hold mode for a predetermined second timeperiod; and if it is determined that said each member of the net hasbeen in the control-hold mode for the predetermined second time period,causing said each member of the net to enter a dormant mode, whereinsaid each member of the net releases its dedicated traffic channel. 2.The method of claim 1, wherein if it is determined that said each memberof the net has not been in the control-hold mode for the predeterminedsecond time period, further including: causing said each member of thenet to return to an active mode, wherein said each member of the netmaintains its dedicated traffic channel, if a member of the net requestsa group call.
 3. In a controller operating in a group communicationnetwork, a method for putting a net into a dormant mode, the methodcomprising: determining whether the net has been inactive for apredetermined time period; causing each member of the net to enter thedormant mode if it is determined that said each member of the net hasbeen inactive for the predetermined time period; and causing said eachmember of the net to cache a state of its service configuration beforeentering the dormant mode.
 4. The method of claim 3, wherein saidcausing said each member of the net to enter the dormant mode includescausing said each member of the net to release its dedicated trafficchannel.
 5. In a controller operating in a group communication network,a computer-readable medium embodying a method for putting a net into adormant mode, the method comprising: determining whether the net hasbeen inactive for a predetermined first time period; if it is determinedthat the net has been inactive for the predetermined first time period,causing each member of the net to enter a control-hold mode, whereinsaid each member of the net maintains its dedicated traffic channel;determining whether said each member of the net has been in thecontrol-hold mode for a predetermined second time period; and if it isdetermined that said each member of the net has been in the control-holdmode for the predetermined second time period, causing said each memberof the net to enter a dormant mode, wherein said each member of the netreleases its dedicated traffic channel.
 6. The computer-readable mediumof claim 5, wherein if it is determined that said each member of the nethas not been in the control-hold mode for the predetermined second timeperiod, the method further including: causing said each member of thenet to return to an active mode, wherein said each member of the netmaintains its dedicated traffic channel, if a member of the net requestsa group call.
 7. In a controller operating in a group communicationnetwork, a computer-readable medium embodying a method for putting thecommunication device into a dormant mode, the method comprising:determining whether the net has been inactive for a predetermined timeperiod; causing each member of the net to enter the dormant mode if itis determined that said each member of the net has been inactive for thepredetermined time period; and causing said each member of the net tocache a state of its service configuration before entering the dormantmode.
 8. The computer-readable medium of claim 7, wherein said causingsaid each member of the net to enter the dormant mode includes causingsaid each member of the net to release its dedicated traffic channel. 9.A controller operating in a group communication network, comprising:means for determining whether the net has been inactive for apredetermined first time period; means for, if it is determined that thenet has been inactive for the predetermined first time period, causingeach member of the net to enter a control-hold mode, wherein said eachmember of the net maintains its dedicated traffic channel; means fordetermining whether said each member of the net has been in thecontrol-hold mode for a predetermined second time period; and means for,if it is determined that said each member of the net has been in thecontrol-hold mode for the predetermined second time period, causing saideach member of the net to enter a dormant mode, wherein said each memberof the net releases its dedicated traffic channel.
 10. The controller ofclaim 9, wherein if it is determined that said each member of the nethas not been in the control-hold mode for the predetermined second timeperiod, further including: means for causing said each member of the netto return to an active mode, wherein said each member of the netmaintains its dedicated traffic channel, if a member of the net requestsa group call.
 11. A controller operating in a group communicationnetwork, comprising: means for determining whether the net has beeninactive for a predetermined time period; means for causing each memberof the net to enter the dormant mode if it is determined that said eachmember of the net has been inactive for the predetermined time period;and means for causing said each member of the net to cache a state ofits service configuration before entering the dormant mode.
 12. Thecontroller of claim 11, wherein said means for causing said each memberof the net to enter the dormant mode includes means for causing saideach member of the net to release its dedicated traffic channel.
 13. Acontroller for providing a dormant mode, comprising: a receiver; atransmitter; and a processor communicatively coupled to the receiver andthe transmitter, the processor being capable of: determining whether thenet has been inactive for a predetermined first time period; if it isdetermined that the net has been inactive for the predetermined firsttime period, causing each member of the net to enter a control-holdmode, wherein said each member of the net maintains its dedicatedtraffic channel; determining whether said each member of the net hasbeen in the control-hold mode for a predetermined second time period;and if it is determined that said each member of the net has been in thecontrol-hold mode for the predetermined second time period, causing saideach member of the net to enter a dormant mode, wherein said each memberof the net releases its dedicated traffic channel.
 14. The controller ofclaim 13, wherein if it is determined that said each member of the nethas not been in the control-hold mode for the predetermined second timeperiod, the processor further being capable of: causing said each memberof the net to return to an active mode, wherein said each member of thenet maintains its dedicated traffic channel, if a member of the netrequests a group call.
 15. A controller for providing a dormant mode,comprising: a receiver; a transmitter; and a processor communicativelycoupled to the receiver and the transmitter, the processor being capableof: determining whether the net has been inactive for a predeterminedtime period; causing each member of the net to enter the dormant mode ifit is determined that said each member of the net has been inactive forthe predetermined time period; and causing said each member of the netto cache a state of its service configuration before entering thedormant mode.
 16. The controller of claim 15, wherein said causing saideach member of the net to enter the dormant mode includes causing saideach member of the net to release its dedicated traffic channel.